Unreliability of Witnesses Means Reliability of Testimony?

Over at Prosblogion, Helen De Cruz gives an engaging analysis of one of scriptures most invoked grounds for conviction, testimony:

“Undefeated testimony: the kind that occurs in the absence of at least the following common and probably most characteristic defeaters: (1) internal inconsistency in what is affirmed, as where an attester gives conflicting dates for an event; (2) confused formulation, a kind that will puzzle the recipient and tend to produce doubt about whether the attester is rightly interpreted or even has a definite belief to communicate; (3) the appearance of prevarication, common where people appear to be lying, evading, or obfuscating; (4) conflict with apparent facts evident in the situation in which the testimony is given, as where a person shoveling earth over smoking coals says there has been no campfire; and (5) (discernible) conflict with what the recipient knows, justifiedly believes, or is justified in believing.” It is a bit ironical that new testament scholars and latter-day defenders of the argument from miracles take the historical perceived unreliability of witnesses as evidence for the reliability of the testimony.